Ionization vacuum pump



June 1, 1965 Filed Feb. 11, 1963 T. A. CONNOR 3,186,632

IONIZATION VACUUM PUMP 3 Sheets-Sheet l 3,186,632 IONIZATIQNVACUUM PUMP Thomas A. Connor-,Hilton, N.Y., assignor to Consolidated Vacuum Corporation, Rochester, N.Y., a corporation of New York Filed Feb. 11, 1963, Ser. No. 257,401 25 Claims. (Cl. 239-69) The present invention relates to the art of evacuation and, more particularly, to improved ionization vacuum pumps.

Ionization vacuum pumps are well known in the art and are sometimes also referred to as ionic vacuum pumps in such enclosure. In most cases, the aforesaid enclosure will have the form of a vacuum-tight envelope of a suitable material, such as glass or metal, having an opening or a pipe member for connection of the envelope to a space or vessel to be evacuated or, usually, to a preevacuated space or vessel to be subjected to further evacuation. In some instances, the aforesaid enclosure may also form part of a vacuum vessel or system confining a pre-evacuated space.

The above-mentioned source of gas molecule-entrapping ice If a-pump according to the invention havinga supply of A gas moleculeentrapping material and two anode structures spaced equally from such source of material is used, a source of electric power supplying two electrically opposed alternating-current voltages of substantially equal magnitude may be employed, and one of such voltages may be applied between the source of material and one of the anode structures and the other of such voltages between the source of material and the other of these anode structures. I

Alternatively, a multi-phase alternating'current source maybe employed and the number of anode structures may be increased accordingly.

Moreover, each anode structure may be provided with I an individual source of gas molecule-entrapping material,

I with all such anode structures being spaced by equal dismaterial may comprise one of the conventional getter maorterials, such as titanium, which has been used most frequently in pumps of this type, or magnesium, aluminum, molybdenum, tantalum,zirconium, barium or various of the rare earths, such as cerium and cerium alloys. In recent years, it has been shown that materials, other than chemically active substances, such as stainless steel, may be capable'of gas molecule-entrapment, provided they are supplied to the pump elements in a quantity sufficient to cause physical entrapment of gas molecules on predetermined surface areas thereof.

Thus, the expression gas molecule entrapping materials as used herein is meant to refer to chemically active getter materials as well as chemically non-active materials which are capable of gas ion entrapment and which do not form compounds that contaminate the vacuum space.

. In accordance with a principal feature of the subject invention, these pumps include a plurality of separate anode structures located in the aforesaid enclosure and spaced substantiallyequally from the above-mentioned source of molecule-entrapping material. These anode structures are electrically insulated from one another so that they may be individually energized by distinct electrical potentials and currents.

In this manner, a plurality of distinct and non-interdependent ionizing areas or electrical discharge paths can be established in the pump space for increased pumping efficiency.

Due to the substantially equal spacing of the anode structures from the source of gas molecule-entrapping material, the latter ionizing areas or discharge paths have closely similar dimensions and impedances.

I have found that the latter features render the pump according to the invention suitable for alternating-current energization.

Thus, I have found that a pump according to the invention can be connected to a source of alternating current, whereby the conventional high-voltage direct-current supply apparatus can be dispensed with.

tances from their corresponding sources of material, and distinct alternating-current voltages may be impressed between such anode structures and their corresponding sources.

The invention will become more readily apparent from the following detailed description of preferred embodiments thereof, illustrated by way of example in the accompanying drawings, in which: I

FIG. 1 is an elevation, in section, of according to the invention;

FIG. 2 is a view along lines IIII of FIG. 1;

' FIG. 3 is a power supply for the pump shown in FIGS. 1 and 2; I

FIG. 4 is an elevation, in section, of a modification of the pump shown in FIGS 1 and 2;

FIG. 5 is a power supplyv for the pump shown in FIG. 4; and 1 FIG. 6 is a modified power supply for the pump shown in FIG. 4.

The pump illustrated in FIG. 1 comprises a housing 10 having an opening 11 and a flange structure 12 for con nection of housing 10 to a vacuum vessel (not shown), such as a pre-evacuated vessel containing residual gas molecules. A mounting or closure plate 13 is attached to a second flange structure 14 by nut and bolt arrangements 15. A sealing member 17, such as a conventional metallic sealing ring, is interposed between plate 13 and flange structure 14. Housing 19 has lateral wall portions 19 defining a central space 2% and a pair of closed nipple members 21 and ZZdefining two chambers 24 and 25 projecting laterally from central space 29 in opposite directions.

A first hollow-cylindrical anode structure 26 is located in chamber 24 and a second hollow-cylindrical anode structure 27 is located in chamber 25. These anode structures 26 and 27 are formed from sheets of Wire mesh material. A bar member 29 and a stud 3h serve as mounting and terminal means for anode structure 26, and a bar member 31 and stud 32 serve as mounting and terminal means for anode structure 27. Terminal and mounting stud 31 extends through a hollow feed-through bushing 34 of a suitable insulating material, such as glass, to the outside of housing 10 to form a terminal 35 for anode structure 26, and terminal stud 32 extends through an in sulating feed-through bushing 36 to the outside of housing 16 to form a terminal 37 for anode structure 27.

A source 40 of gas molecule-entrapping material is disposed in central space 20 of housing Iii. In the embodiment shown in FIGS. 1 and 2, this source 46 comprises a disk 41 of gas molecule-entrapping or getter material, such as titanium. Disk 41 is disposed between anode structures 26. and 2'7 sothat it is spaced by equal distances 0! and d, indicated in FIG. 1, from such anode structures 26 or 27 or, in other words, so that anode structures 26 and 27 are disposed symmetrically with respect to disk 41. Disk 41 has two opposed radial surfaces a vacuum pump 43 and facing, respectively, in the direction of chambers- 24. and and facing, therefore, anode structures 26 i and 27. Considered in a different manner, it will be appreciated that disk 41 extends through a plane-including thelongitudinal axes-of anode structures 26'and27.

lishing an electrical discharge in the spaces between disk I 41 and anode structures 26 and 27 and causing release of gas molecule-entrapping material from disk .41.

- Disk 41 is mounted on a mounting and terminal stud 48 which extends through an insulating bushing 49 disposed in plate 13 and forms a terminal 56 for disk 41 outside of housing 10. Filament-46 is-mounted 'on a pair'of studs 52 and 53 extending through insulating,

bushings 54 and 55 disposed'in plate 13. Studs 52-and 53 7 Operation of the pump shown in FIGS. 1 and 2 is' initiated by connection of the filament 46, disk 41 and anode structures 26 and 27 to a suitablesupply of electric energizing power.

One form of .such supply of electric power is diagrammatically shown in FIG. 3. V

The power supply shown in FIG. 3 comprises a pair ofinput terminals 61 and 62 connected to 'a source of alternating current (notshown); Power supply 64} further includes a first transformer-64 having 'a'primary Winding 65 and a secondary winding 66, a second trans former 68 having a primary winding 69 and a secondary Winding 70, and a third transformer 72 having a primary winding 73 and a secondary winding 74. Primary winding 65*of transformer 64 is connected to input terminals and expensive filament-to-anode rectifiers of the prior-art apparatus can be dispensed with.

The transformer 64 is dimensioned to supply the filament-to-anode potentials required for operation of the 7 pump, while the 'transformer 68 is dimensioned to supply the required filament-to-getter potentiaL The transformer-72 may. be a conventional low-voltage transformer designedto supply heatingcurrent to filament 46.

Operationof the pump shown in FIGS.-1 and 2 is initiated by energizing filament 46 and applying a positive potential to getter disk 41 with respect to filament 46, such as by means of the power source shownin FIG. 3, to cause heating and electron bombardment of disk 41; Dueto this heatingjand electron bombardment, disk 41 will be caused to release gas molecule-entrapping or getter material.

Filament46 and anode structures 26 and 27 are also energized, such'asby. means of} the power'source shown in FIG. 3, so that electrical discharge areas'will be established between filament 46 and anode structures 26 and 27. Gas molecules entering'pump housing) through opening 11 will be ionized in these discharge areas. At the same time, .molecule-entrappinggor getter-particles will be released from. disk 41 and especially from the radical surfaces 43 and 44 thereof. Due to the configuration and positioning ofthese disk surfaces 43 and 44, the latter getter particles will follow two preferred trajectories extending laterally from disk 41' in' the direction of chambers-24 and 25." Since anode structures 26 and 27 are open-ended and hollow and have perforated or wire mesh type wall porti0ns,theparticles following these trajectories will be able toform layers of molecule-entrapping or embedding material95 and 96 in chambers 24 and. 25, respectively, and the ionized gas molecules'will be able to penerate. through anode structures-:26 and 27 to be entrapped or embedded in layers 95 and 96 and thus re- 61 and 62 through a main switch '76. Primary winding 69,of transformer 68 is connected to input terminals, 61 and 62 through an auxiliary switch 77 and main switch 76. Primary winding 73 of transformer 72 is connected to input terminals 61 and 62 through an auxiliary switch 78 and main switch 76. Main switch 76 serves to control the supply of alternating current to allthree transformers 64, 68 and 72, while the auxiliary switches 77 and '78 control the supply of current to the transformers 68 and 72', respectively. I

. Thesecondary winding 66 ,oftransformer 64 is connected to anode terminals 35 and 37 and the secondary winding 74 of transformer 72 to filament terminals 57 and 58 shown in FIG. 1. The secondary winding of transformer 68 is connected toa pair of opposite corners 80 and 81 of a rectifier bridge circuit 82 composed of four rectifier cells 83, 84, 85 and 86. Secondary winding 66 of transformer 64 and secondary winding 74 of transformer 72 have center taps 88 and 39 which are grounded and are connected to one corner 96 of a second pair of opposite corners 90 and91 of rectifier bridge circuit 82. The other corner 91 of said second pair is connected to terminal 50 of disk 41, briefly referred to in FIG. 3 as getter terminal 50.

The rectifier cells 83 to 36 of bridge 82 are poled .so

that a positive potential supplied by the transformer secondary winding 70 will appear on getter terminal 50 with respect to filament 46 during operation of powersupply 60.

It will be understood that the rectifier bridge circuit 82 shown in FIG. 3 need only be dimensioned to rectify the filament-to-getter potential. Due to the rectifying properties of the pumps according to the invention, the large,

moved from the free space within housing 10.

The structure shown in FIGS. .1 andI2 will thus be highly effective to remove gas molecules from the vacuum space and,'consequently, to establish ultra-high vacua.

If desired, the ionization function of the aforesaid discharge .areas can be augmented byumeans of a magnetic field extending throughanode structures27 and 29 and material source 49 in the longitudinal, direction of such discharge areas; This magnetic field maybe established by electrically energized magnet coils disposed on nipple members 21 and 22, such as by coils 97 and 98 shown in dotted lines in FIG. 1. This magnetic field will cause the electrons in the above-mentioned discharge areas to follow substantially helical paths, so that they probability that these electrons will strike and ionize residual gas molecules is increased.

FIG. 4 illustrates'a modification of the pump shown in FIGS. 1 and 2.

The parts of the structures shown in FIG. 4 which are substantially identical to their corresponding parts in FIG. 3 are designated by the reference numerals employed in FIG. 1.

The main difference between-the structures shown in FiGS. 1 and 2 andFIG. 4 resides in the substitution of a pair of getter material sources 100 and 101 for the single getter material source 40 of FIGS. 1 and 2. Thus, in the embodiment shown in FIG. .4, eachanode structure 26 and 27 has associated therewith a disk of gas molecule-entrapping material 103 and 104, respectively, with the spacing d between anodefstructure 27 and disk 104 being substantially equal to the spacing d' between anode structure 26 and disk 103.

Disk 103 is mounted on a stud extending through an insulating bushing 106m plate 13 to provide a terminal107 for disk 103. Disk 104 is mounted on a stud 109 extending through an insulating bushing 1 10 in plate 13 to provide a terminal 111 for disk 104.

The operation of the pump shown in FIG. 4 is similar to the operation of the pump of FIGS. 1 and 2, except that a first voltage is impressed between terminals 35 and 107 and a second voltage between terminals 37 and 111. Preferably, these two voltages are alternating-current voltages that are substantially equal in average magnitude but electrically opposed in phase.

A suitable power supply for the pump of FIG. 4 is diagrammatically shown in FIG. 5.

The circuit shown in FIG. from input terminals 61 and '62 to secondary windings 66, 70 and 74 is identical to the corresponding circuit in FIG. 3 and like reference numerals are employed to designate like parts in such corresponding circuits of FIGS. 3 and 5.

v In FIG. 5, the secondary winding 66 of transformer 64 is again connected to anode terminals 35 and 37, and the secondary winding 74 of transformer 72 to filament terininals 57 and 58. However, the secondary winding 70 of transformer 68 is connected to getter terminals 107 and 111 so that the disk 103 in FIG. 4 will be biased negatively when its corresponding anode structure 26 is biased positively, and so that the disk 104 Will also be biased negati'vely when its corresponding anode structure 27 is biased positively. In addition, the secondary winding 70 has a center t'ap 115 connected to the interconnected and grounded center taps 88 and 89 of secondary windings 66 and 74.

' The operation of the pump of FIG. 4 when energized by the power supply of FIG. 5 will be similar to the operation of the pump of FIGS. 1 and 2, except that the streams of molecule-entrapping material will emerge from two disks 103 and 104, rather than froma single disk 41, and that no rectifying circuit for providing a filament-togetter potential will be necessary.

During operation of the pumps of FIGS. 1 and 2 and of FIG. 4, it may be desirable to provide a negative bias in the vicinity of molecule-entrappinglayers 95 and 96, so that ionized gas molecules are strongly attracted by and securely embedded in layers 95 and 96. When pump housing is made of metal, this negative bias can be simply applied thereto, such as by means of the soldering tab 120 shown in FIG. 4 as being secured to housing 10 by one of the bolts 15. I

FIG. 6 shows a modified form of the power supply shown in FIG. 5. The modified power supply of FIG. 6

is identical in operation and structure to that of FIG. 5, except that it contains, in addition to the parts of the circuit of FIG. 5, a further transformer 125 having a primary winding connected to input terminals 61 and 62 through an auxiliary switch 127 and main switch 76. In addition, transformer 125 has a secondary winding 129 having one end 125' connected to a rectifier device 130 and the other end 129" to a capacitor 131 which is connected with rectifier device 130 through a resistor 133. The interconnected taps 88, 115, and 8? of secondary windings 66, 70 and 74 are connected to the aforesaid other end 129" of secondary winding 129, and the inter connection 134 of capacitor 131 and resistor 133 is connected to housing tab 120 shownin FIG. 4. Rectifier device 130 is poled so that a negative potential will be impressed on tab 120 and housing 10 of the pump shown in FIG. 4.

Should housing 11) be made of glass, an electroconductive surface having terminals for connection thereof to point 134 in FIG. 6 could be provided adjacent layers 95 and 96. In many cases the layers 95 and 96 will be sufiiciently conductive so that they can be directly biased by means of suitable terminals (not shown) extending through the glass envelope. T

While specific embodiments of the invention have been described and illustrated by way of example, it will be understood that various modifications thereof Within the scope of the invention are possible.

Thus, it will be found in many applications that the filament of the pump, such as the filament 46 at the pump shown in FIG. 4 need only be energized during the initial 6 pump operation and that the entrapping material source will be capable of supplying the necessary getter material and the ionizing electrons, once the aforesaid dis- 7 charges are established in the pump.

In addition, it would also be possible to initiate such electric discharges'and the operation of the getter source by means other than a filament, such as by other heat producing or electron bombardment devices.

Furthermore, the pumps according to the invention could also be energizedby direct-current voltages, if de-.

sired.

Other modifications andvariations within the scope of the invention will be apparent to those skilled in the art. I,

I claim:

1. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material in said enclosure, a plurality of separate anode structures insulated from each other, located in said enclosure and spaced substantially equally from said'source of material, and means for applying to each of said anode structures an individul electrical potential with respect to said'source of material, each potential applied to one of said anode structures being distinct from the potentials applied to the others of said anode structures.

2. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material in said enclosure, first terminal means for said source of material extending through said enclosure, at least two separate anode structures in said enclosure spaced substantially equally from said source of material, second terminal means for one of said anode structures extending through said enclosure, third terminal means for the other of said anode structures extending through said enclosure, and means for applying a first voltage between said first terminal means and said second terminal means and for applying a second voltage separate from said first voltage, between said first terminal means and said third terminal means.

3. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material in said enclosure, first terminal means for said source of material extending through said enclosure, at least two separate anode structures in said enclosure spaced substantially equally from said source of material, second terminal means for one of said anode structures extending through said enclosure, third terminal means for the other of said anode structures extending through said enclosure, and means for applying a first voltage between said first terminal means and said second terminal means and for applying a second voltage, separate from said first voltage, between said first terminal means and said third terminal means, said first and second voltages being of substantially equal average magnitude.

4. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material in said enclosure, a plurality of separate anode structures insulated from each other and arranged symmetrically with respect to said source of material, and means for applying to each of said anode structures an individual electrical potential with respect to said source of material to establish a separate electrical discharge between each of said anode structures and said source of material.

5. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said'enclosure to a space to be evacuated, a pair of spaced anode structures insulated from each other and located in said enclosure, a source of gas molecule-entrapping material disposed in the space between said spaced anode structures, andrmeans for providing two separate voltages and for applying'one of said voltages toone of said anode structures and the other of said voltages to the other of said anode structures. t 6. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a plurality of substantially equal average magnitude, andqeach potential applied to one of, said anode structures being dis tinct from the potentials applied to theothers of said anode. structures.

7.- Ah ionization vacuum pump comprising an.enc10-.

sure for'confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material insaid enclosure, a plurality, of hollow anode structures insulated from each otherand locatedin said enclosure,..each of said hollow anode structures having anend portion facing said source of material, with the end portions of said anode structures being spaced by substantially equal distances from said source .of material, and means. for applying to each of said anode structures an individual electrical potential with respect to said source of material.

8. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said. enclosure to a space to be evacuated, a source of gas molecule-entrapping material in said enclosure, at least one pair of spaced, hollow anode structures being insulated from each other, each of said anode struo tures having an end portion facing said source of ma terial, with said source of material being disposed between said anode structures, and means for providing two being insulated from each other .and having their central tion of. one of said anode structures and-for issuing a second, distinct stream of gas molecule-entrapping material in the direction ofv theother'anode. structure, and means for applying a first potential to said one anode structure and'a separate second poten-ti'al to said other anode structure.

i 12. 'An ionization vacuum pump comprisingan' enclosure for confining an evacuated space, means for connectingsaid enclosure toa space to be evacuated, a disk of gas molecule-entrapping material having two radial surfaces, a first'anode structure disposed inthe vicinity of one or saidtwo radial surfaces of saiddisk, a second anode structure insulated from said first anode structure and disposed in the vicinity of the other radial surface of said disk, and' means for applying a first voltage be.-

tween said first anode structure and said disk and'a separate second voltage between said second anode structure and said disk, with said first and second voltages being of substantially equal average magnitude.

13. An ionization vacuum pump comprising an enclosure for confining an evacuated space, said enclosure defining a plurality of laterally disposed chambers, an anode ture disposed. in one of said chambe'rsya second anode structure :disposed in the other of; said chambers, and

axes arranged in a common plane, a source of gas mo1e' cule-en-trapping material disposed between said anode structures and extending through said common plane, and means for providing two separate potentials with respect to said source of material and for applying one of said potentials to one of said anode structures-and the other of said potentials to the other of said anode structures.

10. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a plurality of spaced anode structures insulated. from each other, a

like plurality of sources of gas molecule-entrapping material spaced from said anode structures, each of said .anode structures having associated therewith a said source of material, and means for applying an individual volt- .tage between each of said anode structures audits associated source of material to establish a separate electrical discharge between each anodestructure and its associated source ofmaterial, eachrvoltage applied to one of said anode structures being distinct from the voltages applied to the others of said anode structures.

11. An ionizationvacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a spacetobe evacuated, at least two separate anode structures being insulated from each other and locatedin said enclosure, means for issuing a first stream of gas moleeule-entrapping material in the direcmeans for applyingto said .first anode. structure a first potential with respect to said source. of material and forapplying to said second anode structure a second potential with respect to said source of material.

15L An ionization vacuum pump comprising an enclosure'defining'a central portion with an open end for connection of the: enclosure to a vacuum space, and a pair of oppositely disposedchambersprojecting laterally from said central portion, a disk for gas moleculeentrapping material disposed in said central portion and having a first radial surface facing one of said chambers and a second radial surface facing the other of said chambers, a first anode structure disposed in one of. said chambers, a second. anode structure disposed in the other of said chambers, and means for establishing a first potential between said firstanodestructure and said disk and-a secondpotential between said second anode structure and said disk.

16.:jAn ionization vacuum pump as claimed in claim 15, wherein each of said first and second anode structures has perforated wall portions and Van-opening facing said disk.

17. An ionization pump comprising an enclosure defining a central portion with an open end for connection of the enclosure to a vacuum space, and a pairof oppositely disposed chambers projecting laterally from said central portion, a first disk of, gas molecule entrappin'g material disposed in said central portion and having aradial surface facing one of said chambers, a second diskof gas molecule-entrappingv material disposed in said central portion and having 'a radial surface facing the other of said chambers, a first anode structure disposed in said one chamber, a second anode structure disposed in'said other chamber, and means for applying avoltage between said first disk and said first anode structure and a voltagebetween said second disk and said second anode structure. 1

18. An ionization vacuum pump as claimed in claim 17, wherein each of said first and second anode struc- 9 tures has perforated wall portions and an opening facing said central portion.

19. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material in said enclosure, at least two anode structures in said enclosure spaced substantially equally from said source of material, a source of alternating current providing a pair of substantially equal, electrically opposed alternating current voltages, and means for applying one of said voltages to one of said anode structuresand said source of material and the other of said voltage to the other of said anode structures and said source of material.

20. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material in said enclosure, at least two anode structures located in said enclosure and spaced by substantially equal distances from said source of material, a transformer structure having a primary Winding connectable to a source of alternating current and including a secondary Winding having first and second main terminals connected, respectively, to one and the other of said anode structures, said secondary Winding having a center-tap terminal, and means for connecting said source of material to said center-tap terminal.

21. An ionization vacuum pump comprising an enclosure for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a body of gas molecule-entrapping material in said enclosure, at least two anode structures in said enclosure spaced substantially equally from said body of material,

at least one filament located in the vicinity of said body of material and said two anode structures, a first transformer having a primary winding connected to a source of alternating current and including a secondary winding connected to said anode structures, a rectifier bridge circuit having two pairs of oppositely disposed bridge corners, a second transformer having a primary winding connected to said source of alternating current and including a secondary winding connected to one of said two pairs of bridge corners, a third transformer having a primary winding connected to said source of alternating current and including a secondary winding connected to said filament, said secondary winding of said first transformer and said secondary winding of said third transformer each having a center tap connected to one bridge corner of the other of said two pairs of bridge corners, and the other bridge corner of said other pair being connected to said body of material.

22. An ionization vacuum pump comprising an envelope for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material located in said envelope and including a first and a second body of gas molecule-entrapping material, a first anode struc-- ture located in the vicinty of said first body of material, a second anode structure located in the vicinity of said second body of material, and a source of alternating voltage to said second anode structure and said body of material, said first and second voltages being substantially equal in average magnitude and electrically opposed during the half-cycles thereof.

23. An ionization vacuum pump comprising an envelope for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a first and a second body of gas molecule-entrapping material located in said envelope, a first anode structure located in the vicin ty of said first body of material, a second'anode structure located in the vicinity of said second body of material, a filament located in the vicinity of said first and second bodies of material and said first and second anode structures, transformer means having primary winding means connected to a source of alternating current and including a first secondary Winding connected to said first and second anode structures and having a center tap, a secondary winding connected to said first and second bodies of material and having a center tap, and a third secondary winding connected to said filament and having a center tap, and means for interconnecting said center taps of said first, second and third secondary windings.

24. An ionization vacuum pump as claimed in claim 23, wherein said envelope has a current-conductive inner surface and said transformer means includes meansfor negatively biasing said current-conductive surface with respect to said center taps.

25. An ionization vacuum pump comprising an envelope for confining an evacuated space, means for connecting said enclosure to a space to be evacuated, a source of gas molecule-entrapping material located in said envelope, at least two anode structures insulated from each other and located in said envelope and spaced substantially equally from .said source of material,

means for applying separate potentials to said source of material and said anode structures to establish distrnct electrical discharger between said source of material and said two anode structures, and means for establishing at least one magnetic field extending through said source and said anode structures in the direction of said electrical discharges.

References Cited by the Examiner UNITED STATES PATENTS 3,018,944 1/62 Zaphiropoulos 230-69 LAURENCE V. EFNER, Primary Examiner.

WARREN E. COLEMAN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,186,632 June 1, 1965 Thomas A. Connor It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 25, before "secondary" insert second line 45, for "discharger" read discharges Signed and sealed this 21st day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD]. BRENNER testing Officer Commissioner of Patents 

1. AN IONIZATION VACUUM PUMP COMPRISING AN ENCLOSURE FOR CONFINING AN EVACUATED SPACE, MEANS FOR CONNECTING SAID ENCLOSURE TO A SPACE TO BE EVACUATED, A SOURCE OF GAS MOLECULE-ENTRAPPING MATERIAL IN SAID ENCLOSURE, A PLURALITY OF SEPARATE ANODE STRUCTURES INSULATED FROM EACH OTHER, LOCATED IN SAID ENCLOSURE AND SPACED SUBSTANTIALLY EQUALLY FROM SAID SOURCE OF MATERIAL, AND MEANS FOR APPLYING TO EACH OF SAID ANODE STRUCTURES AN INDIVIDUAL ELECTRICAL POTENIAL WITH RESPECT TO SAID SOURCE OF MATERIAL, EACH POTENTIAL APPLIED TO ONE OF SAID ANODE STRUCTURES BEING DISTINCT FROM THE POTENTIALS APPLIED TO THE OTHERS OF SAID ANODE STRUCTURES. 